#version 300 es
#define S(a, b, t) smoothstep(a, b, t)
precision mediump float;
uniform sampler2D uTextureUnit;
in vec2 vTexCoord;
//输出
out vec4 vFragColor;

uniform vec3 iResolution;
uniform float iTime;
uniform vec2 texSize;

vec3 N13(float p) {
    //  from DAVE HOSKINS
    vec3 p3 = fract(vec3(p) * vec3(.1031, .11369, .13787));
    p3 += dot(p3, p3.yzx + 19.19);
    return fract(vec3((p3.x + p3.y) * p3.z, (p3.x + p3.z) * p3.y, (p3.y + p3.z) * p3.x));
}

vec4 N14(float t) {
    return fract(sin(t * vec4(123., 1024., 1456., 264.)) * vec4(6547., 345., 8799., 1564.));
}
float N(float t) {
    return fract(sin(t * 12345.564) * 7658.76);
}

float Saw(float b, float t) {
    return S(0., b, t) * S(1., b, t);
}

vec2 DropLayer2(vec2 uv, float t) {
    vec2 UV = uv;

    uv.y += t * 0.75;
    vec2 a = vec2(6., 1.);
    vec2 grid = a * 2.;
    vec2 id = floor(uv * grid);

    float colShift = N(id.x);
    uv.y += colShift;

    id = floor(uv * grid);
    vec3 n = N13(id.x * 35.2 + id.y * 2376.1);
    vec2 st = fract(uv * grid) - vec2(.5, 0);

    float x = n.x - .5;

    float y = UV.y * 20.;
    float wiggle = sin(y + sin(y));
    x += wiggle * (.5 - abs(x)) * (n.z - .5);
    x *= .7;
    float ti = fract(t + n.z);
    y = (Saw(.85, ti) - .5) * .9 + .5;
    vec2 p = vec2(x, y);

    float d = length((st - p) * a.yx);

    float mainDrop = S(.4, .0, d);

    float r = sqrt(S(1., y, st.y));
    float cd = abs(st.x - x);
    float trail = S(.23 * r, .15 * r * r, cd);
    float trailFront = S(-.02, .02, st.y - y);
    trail *= trailFront * r * r;

    y = UV.y;
    float trail2 = S(.2 * r, .0, cd);
    float droplets = max(0., (sin(y * (1. - y) * 120.) - st.y)) * trail2 * trailFront * n.z;
    y = fract(y * 10.) + (st.y - .5);
    float dd = length(st - vec2(x, y));
    droplets = S(.3, 0., dd);
    float m = mainDrop + droplets * r * trailFront;

    //m += st.x>a.y*.45 || st.y>a.x*.165 ? 1.2 : 0.;
    return vec2(m, trail);
}

float StaticDrops(vec2 uv, float t) {
    uv *= 40.;

    vec2 id = floor(uv);
    uv = fract(uv) - .5;
    vec3 n = N13(id.x * 107.45 + id.y * 3543.654);
    vec2 p = (n.xy - .5) * .7;
    float d = length(uv - p);

    float fade = Saw(.025, fract(t + n.z));
    float c = S(.3, 0., d) * fract(n.z * 10.) * fade;
    return c;
}

vec2 Drops(vec2 uv, float t, float l0, float l1, float l2) {
    float s = StaticDrops(uv, t) * l0;
    vec2 m1 = DropLayer2(uv, t) * l1;
    vec2 m2 = DropLayer2(uv * 1.85, t) * l2;

    float c = s + m1.x + m2.x;
    c = S(.3, 1., c);

    return vec2(c, max(m1.y * l0, m2.y * l1));
}

void main()
{
    vec4 iMouse = vec4(0.0, 0.0, 0.0, 0.0);
    vec2 fragCoord = vec2(vTexCoord.x * texSize.x - 0.5 * texSize.x, 0.5 * texSize.y - vTexCoord.y * texSize.y);
    vec2 uv = fragCoord.xy / iResolution.y;
    vec2 UV = (fragCoord.xy+.5*iResolution.xy) / iResolution.xy;
    vec3 M = iMouse.xyz/iResolution.xyz;
    float T = iTime+M.x*2.;
    
    #ifdef HAS_HEART
        T = mod(iTime, 102.);
        T = mix(T, M.x*102., M.z>0.?1.:0.);
    #endif
    
    float t = T*.2;
    
    float rainAmount = iMouse.z>0. ? M.y : sin(T*.05)*.3+.7;
    
    float maxBlur = mix(3., 6., rainAmount);
    float minBlur = 2.;
    
    float story = 0.;
    float heart = 0.;
    
    #ifdef HAS_HEART
        story = S(0., 70., T);
        
        t = min(1., T/70.);						// remap drop time so it goes slower when it freezes
        t = 1.-t;
        t = (1.-t*t)*70.;
        
        float zoom= mix(.3, 1.2, story);		// slowly zoom out
        uv *=zoom;
        minBlur = 4.+S(.5, 1., story)*3.;		// more opaque glass towards the end
        maxBlur = 6.+S(.5, 1., story)*1.5;
        
        vec2 hv = uv-vec2(.0, -.1);				// build heart
        hv.x *= .5;
        float s = S(110., 70., T);				// heart gets smaller and fades towards the end
        hv.y-=sqrt(abs(hv.x))*.5*s;
        heart = length(hv);
        heart = S(.4*s, .2*s, heart)*s;
        rainAmount = heart;						// the rain is where the heart is
        
        maxBlur-=heart;							// inside the heart slighly less foggy
        uv *= 1.5;								// zoom out a bit more
        t *= .25;
    #else
        float zoom = -cos(T*.2);
        uv *= .7+zoom*.3;
    #endif
    UV = (UV-.5)*(.9+zoom*.1)+.5;
    
    float staticDrops = S(-.5, 1., rainAmount)*2.;
    float layer1 = S(.25, .75, rainAmount);
    float layer2 = S(.0, .5, rainAmount);
    
    vec2 c = Drops(uv, t, staticDrops, layer1, layer2);
    #ifdef CHEAP_NORMALS
        vec2 n = vec2(dFdx(c.x), dFdy(c.x));// cheap normals (3x cheaper, but 2 times shittier ;))
    #else
        vec2 e = vec2(.001, 0.);
        float cx = Drops(uv+e, t, staticDrops, layer1, layer2).x;
        float cy = Drops(uv+e.yx, t, staticDrops, layer1, layer2).x;
        vec2 n = vec2(cx-c.x, cy-c.x);		// expensive normals
    #endif

    #ifdef HAS_HEART
        n *= 1.-S(60., 85., T);
        c.y *= 1.-S(80., 100., T)*.8;
    #endif

    float focus = mix(maxBlur-c.y, minBlur, S(.1, .2, c.x));
    vec3 col = texture(uTextureUnit, UV+n).rgb;
    // vec3 col = texture(uTextureUnit, n).rgb;
                            // make time sync with first lightnoing

    #ifdef USE_POST_PROCESSING
        t = (T+3.)*.5;			
        float colFade = sin(t*.2)*.5+.5+story;
        col *= mix(vec3(1.), vec3(.8, .9, 1.3), colFade);	// subtle color shift
        float fade = S(0., 10., T);							// fade in at the start
        float lightning = sin(t*sin(t*10.));				// lighting flicker
        lightning *= pow(max(0., sin(t+sin(t))), 10.);		// lightning flash
        col *= 1.+lightning*fade*mix(1., .1, story*story);	// composite lightning
        col *= 1.-dot(UV-=.5, UV);							// vignette

        #ifdef HAS_HEART
            col = mix(pow(col, vec3(1.2)), col, heart);
            fade *= S(102., 97., T);
        #endif

        col *= fade;										// composite start and end fade
    #endif

    //col = vec3(heart);
    vFragColor = vec4(col, 1.);
    //  vFragColor = texture(uTextureUnit,vTexCoord);
}